The present invention relates to turbo-machines, for example gas turbine engines.
During the transient conditions of operation of such machines the temperature of the working fluid in the machine varies relatively quickly, causing those parts of the machine which are close to the working fluid passages to heat up and cool down. For example, in a gas turbine engine compressor or turbine which has a bladed rotor comprising blades mounted on discs and disposed within a casing, the casing is in direct contact with the air or hot gas flowing through the machine and tends to heat up relatively quickly during accelerations of the engine. The rotor discs, however, which are relatively more massive and which are shielded from the hot air by blade platforms and inter-stage spacers, heat up less quickly. The result is differential thermal expansion between the casing and the tips of the rotor blades, carried by the discs, and a consequent loss in efficiency.
It is an object of the present invention to provide a turbo-machine, which is constructed in such a manner that the thermal expansions of the rotors and casings thereof are more nearly matched.